Detecting internal characteristics of light pervious material

ABSTRACT

Apparatus for detecting defects in the core of plywood panels and the like. The apparatus includes transport mechanism for moving a panel along a path, a light source for illuminating one face of a panel moved along the path, and light sensors positioned to sense the amount of light from the source transmitted through a panel. The light sensors produce responses related to the amount of light so transmitted, and such responses are interpreted by electronic circuitry connected to the sensors to indicate the presence of a defect. The invention recognizes that in a plywood panel, different types of defects in the core produce different types of responses and such can be used to segregate panels as to their core defects.

United States Patent [72] Inventor Clifford E. Myers Forest Grove, Oreg. [211 App]. No. 778,545 [22] Filed Nov. 25, 1968 [45] Patented Feb. 23, 1971 [73] Assignee Welsh Panel Company Longview, Wash.

[54] DETECTING INTERNAL CHARACTERISTICS OF LIGHT PERVIOUS MATERIAL 9 Claims, 3 Drawing Figs.

[52] U.S. Cl 250/83.3, 250/219 [51] Int. Cl G0lt 1/16 [50] Field ofSearch 250/83.3 (1R), 83.3 (D), 45.5 (D), 219 (Df); 250/219Df [56] References Cited UNITED STATES PATENTS 3,206,603 9/1965 Mauro 250/83.3

Primary Examiner-Archie R. Borchelt Assistant Examiner-Davis L. Willis AttorneyKolisch and Hartwell ABSTRACT: Apparatus for detecting defects in the core of plywood panels and the like. The apparatus includes transport mechanism for moving a panel along a path, a light source for illuminating one face of a panel moved along the path, and light sensors positioned to sense the amount of light from the source transmitted through a panel. The light sensors produce responses related to the amount of light so transmitted, and such responses are interpreted by electronic circuitry connected to the sensors to indicate the presence of a defect. The invention recognizes that in a plywood panel, different types of defects in the core produce different types of responses and such can be used to segregate panels as to their core defects.

Ill/I/I/l/l/II/l/l IV Ill/III] III/I //l I l// DETECTHJG INTERNAL CHARACTERISTICS OF LIGHT PERVIOUS MATERIAL This invention pertains to apparatus for detecting a defect in the core of a panel. More specifically, it pertains to such apparatus whereby defects are detected through lighting one face of a panel and detecting changes in the amount of light transmitted through the panel to the opposite face thereof. The invention has particular applicability in conjunction with the testing of plywood panels.

in the manufacture today of prefinished panels, such as plywood panels, a tactile grain or other type of pattern is frequently produced in what is to be the outside face of the panel through embossment. In cases where relatively heavy embossrnent is employed, and in order for the final embossed pattern to have good uniformity, it is important that the core layer in the panel, over its entire expanse, afford substantially uniform support for the surface layer being embossed. Nonuniform support is telegraphed by the embossment taking better in some regions than others. Such uniform support is especially important in the case where the outside face of a panel, after embossment, is to be colored, as for example by the process described in U.S. Pat. No. 3,247,047 to Buckley. Any substantial nonuniformity in the embossed pattern is accentuated on coloring of the panel.

This invention recognizes that there are two important types of core layer defects which lead to nonuniform results in a heavy embossing operation. The invention also recognizes that these produce different types of results when scanned using light as contemplated.

One type of defect is known as a core void, and is characterized by a void region in the core layer, such as might result from a crack or a splitin the core veneer or from two core pieces not closely abutting. While core voids vary widely in size, a typical void which would pose a problem might be about 6 or 7 inches long and about one thirty-second to one eighth of an inch wide. A void may, of course, be present in any region of a panel core, but experience has shown that voids are found more commonly near the side margins of a panel.

Typically, the core layer in a plywood panel is made up of successive veneer sheets placed in edge-to-edge abutting relation. Such sheets usually extend completely across a panel, and have widths (measured in the direction of the panels longitudinal axis) of about 4 to 36 inches. The other type of defect mentioned is characterized by the presence in such a core layer of adjacent veneer sheets which differ substantially in compressibility.

In a manufacturer can identify such core defects in a panel before the same undergoes an embossing operation of the type mentioned above, be can use for these panels other prefinishing techniques which are not affected by the defects.

Therefore, a general object of the invention is to provide novel apparatus for detecting in the core'layer of a panel defects of the type described above.

More specifically, an object of the invention is to provide such apparatus which is capable of detecting in the core layer of a panel the presence of a void region, and of regions that differ substantially in compressibility.

Another object is to provide such apparatus which is capable of distinguishing between ru'ultiple types of defects.

According to a preferred embodiment of the invention, a panel is transported through a housing where one face of the panel is illuminated by a light source. Positioned opposite the light source are plural light sensors-more specifically, lightsensitive devices having resistance values that vary with the amount of light that they receive-which respond to the amount of light transmitted through a panel. On a void region in the panel moving past a sensor, an abrupt, short duration change (a substantial increase) occurs in the amount of light received by the sensor, and the latter responds with a related change in its resistance value. The shortness of the change results from the relatively small dimensions of a core void measured in a direction extending across the core pieces or along the length of the usual panel. On successive adjacent core regions that differ substantially in compressibility moving past a sensor, longer duration changes (increases and decreases) occur in the amount of light received by the sensor, and related changes occur in the resistance value of the sensor. Longer duration changes occur with this type of defect s nce the width of the usual veneer sheet or piece in a core substantially exceeds the dimension of a core void when measured as stated above.

Connected to and receiving the responses of the sensors are two follower circuits, one of which responds to short duration changes in sensor resistance (of the type produced by a core void), and the other of which responds to longer duration changes in sensor resistance (of the type produced by core regions of different compressibility). Connected to each follower circuit is a circuit which produces a sustained output signal on the follower circuit. responding to a change in a sensor's resistance.

A further object of the invention is to provide such apparatus which is capable of identifying a core defect quickly, and which thus permits rapid and efficient inspection of a panel.

These and other objects and advantages attained by the invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a simplified fragmentary side elevation illustrating apparatus constructed according to the invention;

FIG. 2 is a view taken along the line 2-2 in FIG. 1; and

FIG. 3 is a schematic diagram, partly in block form, illustrating electrical circuits employed in the apparatus of FIGS. 1 and 2.

Turning now to the drawings, and referring first to FIGS. 1 and 2, indicated generally at 10 is apparatus as contemplated herein for detecting a defect in the core of a panel. The apparatus comprising a housing 12 including upright front and rear walls l4, 16, respectively, joined at their opposite sets of ends by upright sidewalls l8. Walls 14, 16 are provided with elongated, transversely extending openings 20, 22, respectively (shown in FIG. 1). The housing further includes top and bottom pieces 24, 26, respectively, suitably joined to the front, rear and sidewalls. The inside surfaces of the parts making up the housing are suitably coated, as by painting, with a coating which has a minimum reflectivity (such as a dull black coating).

Suitably mounted adjacent the front and rear ends of the housing are pairs of vertically spaced power-driven rolls, such as rolls 28. The rolls are driven in any suitable fashion in the direction indicated by the arrows on the rolls. Rolls 28 serve to transport a panel, such as plywood panel 30, through the housing in the direction of arrow 32 (FIG. 1).

Mounted inside housing 12, on supports 34 which are fastened to sidewalls 18, is a flat, substantially horizontal, clear glass plate 36. Plate 36, together with rolls 28, constitute transport means for moving panels through the housing along a defined path, such rolls and plate also being referred to as support means for panels. The panels are moved longitudinally,or in the direction of the grain in the faces and backs, such direction being one that extends across the grain of the core.

Suitably mounted inside the housing beneath plate 36 are plural incandescent spotlights, such as spotlights 38, located at points spaced across the width of the housing. The spotlights, also referred to herein collectively as a light source, function to illuminate the bottom surface of a panel overlying plate 36. Spotlights 38 are conventional units which produce light within the infrared spectrum as well as within the visible spectrum.

Disposed above plate 36 at points spaced along a line overlying lamps 38 are plural light sensors, in the form of light-sensitive resistance devices 40. Devices 40, collectively constituting light-sensing means, are supported on an elongated mounting 42. The devices are more closely spaced adjacent the ends of the mounting (as can be seen for the left end of the mounting in H6. 2) than they are in the region between the mountings ends. For example, the devices might be spaced about 1 inches apart near the ends of mounting 42, and about 5 %inches apart elsewhere. This is to take care of the fact, mentioned earlier, that voids are more commonly found near the side margins of a panel. Although different numbers of devices 30 may be employed, a typical number might be about 1 l or 12 Where the panels to be scanned are about 4 feet wide.

Preferably, each device 40 comprises a semiconductor diode, known as a photo-duo-diode, which is sensitive primarily to infrared light. Such a diode hasa resistance value which varies inversely with the amount of infrared light shining on it, and in addition, is capable of responding very rapidly (as quickly as about one-millionth of a second) to a change in the amount of such incident light. A variation in the resistance value of a diode ill herein is referred to as an electrical response of the diode. A particular diode which has been found to perform satisfactorily is one made commercially by Texas instruments lnc. known as a Type -38, N-P-N diffused silicon photo'duo-diode, described in Techanical Bulletin No. Dir-S 622927, Jul. 1962.

Also disposed above plate 36 is a pairof diodes 44 supported on projections 46 that extend from front and rear sides of mounting 42. Diodes 44 are similar to diodes 40, and are employed, as will be more fully described, to indicate when a panel is interposed between spotlights 38 and diodes 40.

Referring now to FIG. 3, indicated generally at 48, 50 are follower circuits, and at 49, 51 are sustaining circuits, constructed according to the invention. At 52 is a circuit for detecting the presence of a panel inside housing 12.

Circuit 48 includes a pair of transistors 54, 56. Circuit 49 comprises a silicon-controlled rectifier 58, and a relay 6t). Relay 60 includes a solenoid 60a and a normally open switch 601:.

The emitter of transistor 54 is connected directly to a positive voltage supply conductor 62, and to the emitter of transistor 56 through a diode 66. Negative voltage from a negative voltage supply conductor 67 is supplied the collector of transistor 54 through a resistor 6%, and is supplied the base of the transistor through resistors 70, 72. Resistor 72 is variable. The base and collector of transistor 54 are connected through a capacitor '74.

Transistor 56 has its base connected directly to the collector of transistor 54, and its collector connected through a resistor 76 to the gate of rectifier 58. The cathode of rectifier 58 is connected directly to conductor 67, and the anode of the rectifier is connected through a conductor 80 to one end of solenoid 60a. The other end of the solenoid is connected through a normally open switch 82b to conductor 62. Switch @Zb forms part of a relay 82 which further includes a solenoid 82a and another normally open switch 82c.

Follower circuit 50 and sustaining circuit 51 are similar in some respects to circuits 48, d9, respectively. Thus, circuit 50 includes transistors 84, 86 which correspond to transistors 54, 56. Circuit 5i includes a silicon-controlled rectifier 88 corresponding to rectifier 58, and a relay 99 corresponding to relay fill. Relay 90 includes a solenoid 9ila and a normally open switch 901:. The various components in circuits 50, 51 are interconnected in substantially the same fashion as the corresponding components in circuits 4%, 49, except that there is no capacitor in circuit 50 corresponding to capacitor 74 in circuit 4%. The lower end of solenoid 90a in circuit 51 is connected to conductor 62 through switch 820.

Describing the connections existing between diodes 40 and circuits 48, 50, the diodes, only two of which are shown for illustration purposes in H6. 3, are connected electrically in parallel between conductors 92, M. To take care of minor in ternal differences in the resistance values which diodes dll have under similar conditions of illumination, each diode is provided with a compensating circuit including a variable resister 96 and a capacitor 98 connected in series with the diode. The resistor in each compensating circuit permits adjustment to correct for a resistance difference of the type mentioned, and the capacitor affords DC isolation between the diodes to permit independent adjustment of the variable resistor for each diode.

Conductor 94 is connected to previously mentioned conductor 62. Conductor 92 is connected to the base of transistor 5&- through a capacitor Mil, and is connected to the base of transistor 84 through a diode 102 and a capacitor we. Capacitor 100 has a substantially smaller capacity than capacitor W4.

Circuit 52 includes a pair of transistors W6, M8. The emitter of transistor 106 is connected directly to conductor 62, and the collector is connected through a resistor lltl to conductor 67. The base of transistor 196 is connected through resistors M2, 114 to conductor 62, and through resistor M2, the parallel combination of diodes M, and a resistor 116 to conductor 67. Resistor 114 is variable.

The base of transistor W8 is connected directly to the collector of transistor 106, and the emitter of transistor ltltl is connected through a diode 1 18 to conductor 62. The collector of transistor 10% is connected through solenoid 82a to conductor 67.

Explaining now how the apparatus described herein operates, it will be noted that diodes ll) are connected in such a fashion to the bases of transistors 54, 84, that a change in the resistance value of a diode tends to produce a related change in the level of the voltage applied to such bases. Because of the presence of capacitors 98, 100, 104, such a resistance value change produces a temporary, rather than a lasting, change in the DC voltage applied to the bases in the transistors. More specifically, a resistance value change of the type mentioned tends to produce a voltage pulse at the bases.

Because of the capacity difference mentioned earlier between capacitors 100, 104, only a relatively short duration pulse (occurring within a time span of about one-thousandth of a second) can occur at the base of transistor 54. Conversely, only a longer duration pulse can occur at the base of transistor 34.

Resistor 72 in circuit 4%, and the corresponding resistor in circuit 50, are adjusted to place bias voltages on the bases of transistors 54%, 84 sufficient to cause these transistors norm ally to conduct. For reasons which will become apparent, the bias voltage on the base of transistor 54 is adjusted to a considerably higher value than that on the base of transistor 84. A typical value for the former might be about l.0 volts, and a typical value for the latter might be about 0.3 volts. With transistors 54, 84 conducting transistors 56, 86,and rectifiers 58, 88 normally are in nonconducting states.

Resistor 114 in circuit 52 is adjusted whereby so long as light from spotlights 38 shines on at least one of diodes 44, transistor 106 conducts. With transistor 106 conducting, transistor 108 is held in a nonconducting state. Relay solenoid 82a is nonenergized, and switches 82b, 820 are open.

Considering a defect scanning operation, rolls 28 adjacent the infeed end (left side in in H6. 1) of housing 12 grab the lead edge of a panel, and move the panel into the housing preferably at a speed of about 375 to 400 feet per minute. On the panel reaching a position such as position 30A shown in dash-dot outline for panel 30, light from spotlights 3b is blocked from diodes 44. When this occurs transistor 106 turns off, and transistor 108 turns on energizing solenoid 82a. Switches 82b, 82c thereupon close and apply positive bias voltage through solenoids 60a, a to the anodes of rectifiers 58, 88.

As the panel continues through the housing, if a core void passes beneath one of diodes 40, the diodes resistance value drops abruptly for a very short period of time (less than onethousandth of a second), and causes a positive voltage pulse to occur at the base of transistor 54. The amplitude of the pulse is sufficient to counteract the negative bias voltage at the base, and as a consequence, the pulse causes transistor 54 momentarily to turn off. The pulse is of too short a duration to pass through capacitor 104 to the base of transistor 84.

On transistor 54 momentarily turning ofi, transistor 56 switches momentarily to a conducting state, and thereupon places rectifier S8 in a conducting state. This results in solenoid 60a being energized and closing switch 60b. Regardless of what thereafter occurs in transistors 54, 56, rectifier 58 continues to conduct, and solenoid 60a remains energized, so

long as switch 82b remains closed. Switch 8212 will open on the trailing edge of the panel moving to a position exposing one of diodes 44 to light from spotlights 38.

Closure of switch 60b, therefore, is effective to produce an output signal, and may be employed to indicate the presence of a core void in a panel.

if, instead of a core void, core regions of considerably differing compressibility pass between the spotlights and diodes 4i), relatively long duration resistance value changes occur in one or more of the diodes. Such a change results in the application of a positive voltage pulse at the base of transistor 84 sufficient to turn the transistor off. The amplitude of such a pulse is considerably less than that of a pulse produced by a core void. This is because a core void produces a much greater change in a panels perviousness to light. Because of its relatively small amplitude and its long duration, the pulse does not affect transistor 54.

On transistor 84 momentarily turning off, transistor 86 switches momentarily to a conducting state, and places rectifier 88 in a conducting state. Solenoid 90a thereupon becomes energized and closes switch 9%. So long as switch 82c remains closed, current continues to flow through solenoid 90a and rectifier 88 regardless of the conditions of transistors 84, 86. Switch 82c opens under the same conditions that cause opening of switch 82b.

Closure of switch 90b is effective to produce an output signal indicating the presence in a panel core of regions that differ considerably in compressibility.

Thus, the invention proposes novel apparatus for detecting the presence of certain types of defects in the core of a panel which affect the light perviousness of the panel. With detection accomplished through diodes 40 which respond continuously and rapidly to changes in the amount of light transmitted through a panel, relatively quick and efficient scanning for defects (even very small ones) is possible. For example, utilizing apparatus constructed according to the invention, panels have been successfully scanned when moving at speeds of up to 400 feet per minute. Core voids having a dimension longitudinally of the panel as small as one sixty-fourth of an inch have been detected at such a speed.

Because of the differences in the electrical responses produced in diodes 40 by the two different types of defects, and because follower circuits 48, 50 are each constructed to respond to only one type of diode response, the apparatus readily distinguishes between the defects.

Although defects passing through housing 12 produce only momentary responses in the follower circuits, the novel sustaining circuits proposed herein take care of this by producing from such momentary responses sustained output signals. Thus, one is assured of knowing when a particular panel has a defect.

The number and relative spacing of diodes, such as diodes 40, employed may, of course, be varied to take care of different situations.

While an embodiment of the invention has been described herein, it is appreciated that changes and variations may be made without departing from the spirit of the invention.

I claim:

1. ln apparatus for detecting the internal characteristics of a light-pervious panel including transport means for moving a panel along a path, and a light source which produces light within the infrared spectrum disposed on one side of said path operable to illuminate one face of a panel moved along the ath' p plural light-sensitive devices sensitive to light within such spectrum disposed on the opposite side and distributed transversely of said path positioned to receive light from the source transmitted through a panel, each light-sensitive device producing continuously an electrical response varying with changes in the amount of light received by the device;

compensating circuit means operatively connected to said light-sensitive devices compensating for differences in the electrical responses produced by the devices with each receiving a given amount of light;

follower circuit means connected to said light-sensitive devices and sensing their said continuous responses, generating a momentary response on a certain variation occurring in the continuous response of a device; and

sustaining circuit means connected to said follower circuit means triggered by such a momentary response and producing when so triggered a sustained output signal.

2. The apparatus of claim 1, wherein a light-sensitive device comprises a resistance device whose resistance value depends upon the amount of light shining on the device.

3. The apparatus of claim 1, wherein said light-sensitive devices are connected electrically in parallel.

4. The apparatus of claim 3, wherein each device, with a given amount of light shining on it, has a certain resistance value, and said compensating circuit means compensates for differences in said certain resistance values with said devices each receiving said given amount of light.

5. The apparatus of claim 4, wherein said compensating circuit means comprises for each device an adjustable resistor connected in series with the device.

6. The apparatus of claim 5, wherein said compensating circuit means further comprises for each device a capacitor connected in series with the device. I

7. The apparatus of claim 1, wherein said follower circuit mean includes a transistor which switches to a conducting state on said certain variation occurring in said continuous response, and said sustaining circuit means includes a siliconcontrolled rectifier operatively connected to said transistor and placed in a conducting state on the transistor switching to its said conducting state.

9. ln apparatus for detecting the internal characteristics of light-pervious material including transport means for moving such material along a path, and a light source disposed on one side of said path operable to illuminate one side of material moved along the path;

light-sensing means disposed on the opposite side of said path positioned to receive light from the source transmitted through material moved along the path, said lightsensing means producing an electrical response varying with changes in the amount of light received;

a first follower circuit connected to said light-sensing means sensing its said response and producing an output signal when a variation occurs in said response which takes place within one span of time; and I a second follower circuit connected to said light-sensing means sensing its said response and producing another output signal when a'variation occurs in said response which takes place within another span of time. 

1. In apparatus for detecting the internal characteristics of a light-pervious panel including transport means for moving a panel along a path, and a light source which produces light within the infrared spectrum disposed on one side of said path operable to illuminate one face of a panel moved along the path; plural light-sensitive devices sensitive to light within such spectrum disposed on the opposite side and distributed transversely of said path positioned to receive light from the source transmitted through a panel, each light-sensitive device producing continuously an electrical response varying with changes in the amount of light received by the device; compensating circuit means operatively connected to said lightsensitive devices compensating for differences in the electrical responses produced by the devices with each receiving a given amount of light; follower circuit means connected to said light-sensitive devices and sensing their said continuous responses, generating a momentary response on a certain variation occurring in the continuous response of a device; and sustaining circuit means connected to said follower circuit means triggered by such a momentary response and producing when so triggered a sustained output signal.
 2. The apparatus of claim 1, wherein a light-sensitive device comprises a resistance device whose resistance value depends upon the amount of light shining on the device.
 3. The apparatus of claim 1, wherein said light-sensitive devices are connected electrically in parallel.
 4. The apparatus of claim 3, wherein each device, with a given amount of light shining on it, has a certain resistance value, and said compensating circuit means compensates for differences in said certain resistance values with said devices each receiving said given amount of light.
 5. The apparatus of claim 4, wherein said compensating circuit means comprises for each device an adjustable resistor connected in series with the device.
 6. The apparatus of claim 5, wherein said compensating circuit means further comprises for each device a capacitor connected in seRies with the device.
 7. The apparatus of claim 1, wherein said follower circuit mean includes a transistor which switches to a conducting state on said certain variation occurring in said continuous response, and said sustaining circuit means includes a silicon-controlled rectifier operatively connected to said transistor and placed in a conducting state on the transistor switching to its said conducting state.
 9. In apparatus for detecting the internal characteristics of light-pervious material including transport means for moving such material along a path, and a light source disposed on one side of said path operable to illuminate one side of material moved along the path; light-sensing means disposed on the opposite side of said path positioned to receive light from the source transmitted through material moved along the path, said light-sensing means producing an electrical response varying with changes in the amount of light received; a first follower circuit connected to said light-sensing means sensing its said response and producing an output signal when a variation occurs in said response which takes place within one span of time; and a second follower circuit connected to said light-sensing means sensing its said response and producing another output signal when a variation occurs in said response which takes place within another span of time. 